Manufacture of active carbon



Patented Mar. 2%, 1953 2,es2,7ss AN crrunii or ACTIVE oAnnon No Drawing.

Our present invention relates to the manufacbon" now manufactured is'derived from the'waste liquors fromtitli'ecooking of wood to form pulp 'lfor'jpaper makingi This liquor; known in the 'fpjaper'jiiidustry as 'blacliliquor; containslthat pertionof the'jwood which was rendered soluble .by cooking" it with alkaline solutions, more especi lly witu'redium: hydroxide "or sodium hydroxide en'- isjconceritrated and then burned for the recov jeryof. salts which it contains. When "it"is procle'ssed'forithe,recovery'of'active carbon it is caused .to. unaerge partial combustion usually in kilns "of the rotary type in which the organic material i is, for the most part, carbonized. 'Thecarbbnized material, termed blackv ash, is then lixivi'ated to remove the soluble salt's' 'and the crude carbon ,plidduct .tHehTfilT-thel"purified and activated;

,corpor'ating'ini the black liquor "asuitable amount ,o'fiadded'"organic; i. 1' e1", carbonaceous material. enti iiisbased upon oundiscoverythat organic mat}jer'ijal l in? "the black" liquor the i'added carbonaceous "material" will"'also yield" carbon which is susceptible to the same or comparable degreeof acti'va on asthebrganic'material orig- .inally present-m thebla ckliqiidri'""Apparently lZe'd'end therifiubjedtdto activation in the usual my??? m y active carbon isms.

-11." z-gu ie. 1.; in; 1 Q: j bfi y out our invention we may incor r ate e" r ed comminuted carbonaceousmaal i fl f el trated black liquor of 's'ay bCSS'eduhdef'th'Saime conditions as'th'e total solids 'morefor less'which' is "the concentra- William E. McMinnJ'Iymne, West Virginia Pulpjanil Paper N. Y., a corporation of Application October 12, 1 949, 1'- iaINo- 1, 21s0 i v- 7 Gag... (estee -421) laboratory ball mill so as to pass an 8-.mesh screen?- It was thereuponmixed-with black liq- 'u'or -at totar 'stouds 03 i *B alt-160 :02) and 21-6 "gramspe'r liter alkalinity in the ratio of -1 part by weight of purebark to 10 parts byweight oI blacK' liquor. In" other words," black liquor sends-1 1a the amount 'ofi 5i5 partsin'black liquor were mixed with l part of barks-100 grarn'sof this iii-ixturewas car'b'cnizc-idat 400 C.-500 C. without-access "to air, ""and =then roasted at from Q-950 C., this additional oxidation step at the higher temperaturerendering the subsequent active'i-tion' step" more *efiective. The" black ash formed was-leached withfliot water and the" crude caIr ii eeuvated by selective oxidation "with stearii atf800 950 0., followed by air at from 1400-600? 0. I i The activation was carried to a point where the yield was 3.5% dfamixtu're started with on a dry basis." The active carbon' so produced gave a' molasses value" of S3. "When grams of the same black"liduorcontainingnd' barkfiwas processed iii the same manner, the carbon produced had aTsimilar molasses value of 83 and" with ap proximately the same recover-y. Although the recovery was approximately' the same-in .both instances, the yield was greater in the case of the mixture containing bark because of the higher concentration of the organic material in the starting substances. Similar experiments with ground hardwood bark gave equally satisfactory results. 1

The molasses test is one much used by sugar refineries for evaluating active carbon, and it is particularly indicative of the ability oi the carbon to remove color 'bodies'from many other products. Inasmuch as different batches of blackstrap molasses vary in composition depending on the source from which they are obtained, it is difficult to standardize the exact experimental conditions, particularly the concentration. Becauseot this, the molasses value (M. V.) rep-'- resents the relative value of one carbon in terms of a reference carbon. The molasses values stated here are all based on a comparison to the samestandard commercial active carbon. mm e :Z -WQQQ seweusiimdr ed a ontaini g 40% moisture and passing a 4-mesh screeniw'as added to 'a screw conveyor carrying black "square; a rotary kiln in the pulp mill in varying amounts to produce a feed mixture to the rotaryki-lnof from Oflfi pound sawdust per gallon' (if-black liquor to 0.64 pound per "gallon: After burn "the rotary kiln atmaximum temper- At this stage of the process, the carbon has very little ability to adsorb molasses color, but a test known as the iodine test is of value in indicating whether the carbon at this stage can be subsequently activated to produce a satisfactory decolorizing carbon for molasses. In general, the higher the iodine value, the more readily does the carbon activate and the data in the table indicate that increasing amounts of sawdust in the black liquor gave an equal or greater iodine value and hence produced a product that would be readily activated in a subsequent acti vation. This conclusion was confirmed since the leacher from the black ash was satisfactorily activated in plant operation.

For the carrying out of the method according to this example it is desirable to insure thorough mixing of the black liquor and added finely divided carbonaceous material. For this purpose a dough or plaster mixer or other similar type apparatus may be used, which will fold in the finely divided solid material in the black liquor.

Example 3.Samples of bituminous coal occurring locally (Tyrone, Pa.) were finely ground and mixed with black liquor of 55% total solids (34 B. at 60 C.) and 216 grams per litre causticity, after which the mixture was carbonized and subjected to activation at high and low temperatures. The following schema-tic representation shows the steps performed:

Recovery, 70%.

Low temperature activation at 400-600 C. with 50% recovery.

30 grams of finished product having an M. V. (molasses value) of 90.

When the acid washing step was omitted, with the other steps remaining the same, an M. V. of

58 was had.

The M. V. value of 90 above obtained was superior to the value obtained by processing coal alone in the same manner, a typical value for which with conditions otherwise substantially the same is 40 M. V.

It will be noted that when carrying out the invention on a laboratory scale it is preferred to conduct the preparation of the black ash in two stages, i. e., a charring stage in which the heating is done without access to air, and a roasting stage where air is admitted. Thereby the oharring may be done without appreciable oxidation, which is desirable since oxidation at lower temperatures is not as effective in producing a final activated product as is oxidation at the higher temperatures. When operatin on a commercial scale, on the other hand, the operations of charring and roasting may be combined, since the charring will take place so rapidly that any oxidation taking place will not affect the result appreciably.

It will be seen from the foregoing that when carbonaceous material, as represented by bark and sawdust, was added to black liquor and the mixture processed to obtain activated carbon, the degree of activation of the carbon obtained was on the whole greater than when the black liquor alone was used. The use of coal as an extender gave a product that was within the range obtainable from black liquor solids alone with substantially the same degree of burning away of the carbon present. Provided that not substantially more than one part of bark, for example, is used to ten parts by weight of black liquor of 55% solids, the parts being by weight, little change in the normal process of making active carbon from black liquor is required, such additional steps being merely the grindin of the bark or other extender, screening it and mixing it with black liquor.

We claim:

1. In the method of making active carbon from black liquor in which the black liquor is concentrated, burned to black ash, the carbon recovered therefrom and activated, the improvement which consists in: admixing with the concentrated black liquor comminuted carbonaceous material to form a substantially homogeneous fiowable mixture, such carbonaceous material serving as an extender for the carbon contained in the black liquor, and increasing the yield of active carbon obtained.

2. The method according to claim 1 in which the added carbonaceous material is bark.

3. The method according to claim 1 in which the added carbonaceous material is coal.

4. The method according to claim 1 in which the added carbonaceous material is bark in the proportions of approximately 5.5 parts black liquor solids in black liquor to 1 part of bark.

5. In the method of making active carbon the steps which consist in: admixing concentrated black liquor with comminuted bark in the proportion of not substantially more than 1 part by Weight of bark to 5.5 parts of black liquor solids in black liquor, to form a substantially homogeneous flowable mixture subjecting the mixture to partial combustion at a temperature not substantially less than 400 C. and not substantially in excess of 500 C. and then roasting at not substantially less than 750 C. and not substantially more than 950 0., leaching the product so formed to remove water soluble salts, then activating the carbonized material so obtained.

6. In the method of making active carbon the steps which consist in: admixing concentrated black liquor with comminuted coal to form a substantially homogeneous fiowable mixture, carbonizing the mixture at a temperature not substantially less than 400 C. and not substantially activatingby heating to not substantially less than 800 C. and notsubstantially beyond 900 C. in the presence of air.

7. In the method of making active carbon, the x 1 steps which consist in: admixing concentrated black liquor with comminuted carbonaceous material in the proportion of not substantially more than one part comminuted material to 5.5 parts of blaek liquor solids in black liquor, to form a substantially homogeneous fiowable mixture subjecting the. mixture to partial combustion at maximugn temperatures substantially in the range of 900 to 1100 0., leaching the product so formed to remove water soluble salts, and then activating the carbonized material so obtained.

JOHN W. HASSLER.

WILLIAM E. MoMINN.

6 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,383,755 Punnett et al July 5, 1921 1,462,752 Jacobs July 24, 1923 1,483,160 Creighton Feb. 12, 1924 1,504,730 Whitaker Aug. 12, 1924 1,527,083 Schmidt Feb. 17, 1925 1,547,037 Hene July 21, 1925 FOREIGN PATENTS Number Country Date 435,345 Great Britain -1 Sept. 19, 1935 

1. IN THE METHOD OF MAKING ACTIVE CARBON FROM BLACK LIQUOR IN WHICH THE BLACK LIQUOR IS CONCENTRATED, BURNED TO BLACK ASH, THE CARBON RECOVERED THEREFROM AND ACTIVATED, THE IMPROVEMENT WHICH CONSISTS IN: ADMIXTING WITH THE CONCENTRATED BLACK LIQUOR COMMINUTED CARBONACEOUS MATERIAL TO FORM A SUBSTANTIALLY HOMOGENEOUS FLOWABLE MIXTURE, SUCH CARBONACEOUS MATERIAL SERVING AS AN EXTENDER FOR THE CARBON CONTAINED IN THE BLACK LIQUOR, AND INCREASING THE YIELD OF ACTIVE CARBON OBTAINED. 